Rubber-based composite material and the rubber article using the same

ABSTRACT

A rubber based composite material having a rubber composition and, adhered thereto, a reinforcing material having a coating film containing a metal or a metal compound capable of reacting with sulfur formed on the surface of the material, characterized in that the oxygen content in the coating film increases toward the reinforcing material in the thickness direction.

TECHNICAL FIELD

The present invention relates to a rubber-based composite materialcomprising a rubber and a reinforcing material adhered to each other,and the rubber article using the same, and in particular, to arubber-based composite material excellent both in initial adhesivenessand adhesion durability under a wide range of vulcanization conditionand the rubber article using the same.

BACKGROUND ART

Reinforcing materials such as organic fiber codes and steel codes havebeen widely used hitherto in rubber-based composite materials for use intire, belt, hose, and the like. In such a case, it is very importantthat the rubber and the reinforcing material bind to each other firmly,from the viewpoints of the durability and the morphological stability ofproduct. For example, in composite materials of an organic fiber codeand a rubber, the organic fiber code is commonly dipped in anresorcin-formaldehyde condensate/latex (RFL) adhesive for improvement inadhesion between the two, while in composite materials of a steel codeand a rubber, the steel code is plated in various ways for improvementin adhesion between the two.

In this manner, there are a variety of ways to improve the adhesivenessbetween a rubber composition and a reinforcing material, and suchcomposite materials higher in adhesiveness should ideally be superiorboth the initial adhesiveness and the adhesion durability.

SUMMARY OF THE INVENTION

However, there existed a problem that increase in the adhesiondurability between a rubber composition and a reinforcing material isoften accompanied with decrease in initial adhesiveness under certainconditions while increase in the initial adhesiveness under widervulcanization conditions leads to decrease in the adhesion durability.

Considering the circumstances above, an object of the invention is toprovide a rubber-based composite material excellent both in initialadhesiveness and adhesion durability under a wide range of vulcanizationcondition.

The present invention provides a rubber-based composite materialproduced by adhering a rubber composition to a reinforcing materialhaving a film containing a metal or a metal compound capable of reactingwith sulfur formed on the surface of the material, characterized in thatthe oxygen concentration in the film increases toward the reinforcingmaterial in the thickness direction.

The film may be a laminate of two or more layers different in thecomposition ratio of metal and oxygen, and the ratio of oxygenconcentration to metal concentration in the layer at the reinforcingmaterial side of the film is preferably 1.5 times or more larger thanthe ratio of oxygen concentration to metal concentration in the layer atthe film surface side.

The reinforcing material according to the present invention ispreferably an organic fiber, and more preferably, the organic fibercomprises at least one of polyester and polyamide. In addition, thereinforcing material of the invention is preferably a non-woven fabric.

The film is preferably formed by physical vapor deposition (PVD) orchemical vapor deposition (CVD), and the physical vapor deposition (PVD)method is more preferably a magnetron sputtering method.

The metal or metal compound in the film is preferably cobalt or cobaltoxide.

In addition, the invention includes rubber articles using therubber-based composite material above.

The invention described above provides a rubber-based composite materialhaving a rubber composition and a reinforcing material adhered to eachother that is excellent both in initial adhesiveness and adhesiondurability under a wide range of vulcanization conditions.

This application claims benefit of and priority to Japanese PatentApplication No. 2002-150582, filed on May 24, 2002, which isincorporated herein by reference in its entirety for all purposes.

DESCRIPTION OF THE PREFERRED EMBODIMENT

Hereinafter, the present invention will be described in detail.

The reinforcing material for use in the rubber-based composite materialaccording to the invention is not particularly limited, and examplesthereof include metals or the alloys thereof such as iron, nickel,copper, tin, zinc, and lead; natural polymer fibers such as cotton,rayon, and cellulose; synthetic polymer fibers such as polyester,polyvinyl alcohol, polyimide, and polyamide; known nonmetal materialssuch as plastics and ceramics; and combinations of the metal or alloyand the nonmetal material above. Preferable is a natural or syntheticpolymer fiber, and particularly preferable is a polyester or polyamidefiber. The polyester fibers include polyethylene terephthalate fiber,polyethylene-2,6-naphthalate fiber, polybutylene terephthalate fiber,and the like. The polyamide fibers include aliphatic polyamide fibersrepresented by various nylons; aromatic polyamide fibers represented byp-diaminobenzene terephthalamide, p-diaminobenzene isophthalamide, ando-diaminobenzene-2,6-naphthylamide; and the like.

The shape of the reinforcing material is not particularly limited andmay be freely determined according to applications, and examples thereofinclude non-woven fabric, woven fabric, code, and the like, oralternatively, a fiber filament having the film according to theinvention may be blended to the rubber composition as it is.

Non-woven fabrics have advantages not only as a reinforcing material butalso as a light-weight material, and thus application thereof to avariety of rubber articles that demand rigidity and durability has beenstudied, and application of the non-woven fabrics to the rubber-basedcomposite materials that did not contain such a reinforcing material ishighly expected, as it allows expansion of the freedom in designing andimprovement in durability of such materials. The non-woven fabrics arewebs produced, for example, by carding, papermaking, air laying, meltblowing, or spun bonding, without twisting or weaving a number of fiberbundles. Favorable examples of the methods of bonding the fibers in webexcept the melt blowing or spun bonding method include heat-sealingmethod, binder method, and water jet entangling or needle punch methodof entangling fibers with running water or needle. In particular,non-woven fabrics produced by the water jet entangling or needle punchmethod of entangling fibers with running water or needle, melt blowingmethod, and spun bonding method are preferable. In addition, amultilayer structured filament fiber in which a material differs from anadjoining layer may also be used. Further, composite fibers may also beused such as core-in-sheath structure having different materials in thecore and sheath, a radial pattern, or in the shape of petals, layers, orthe like.

The non-woven fabric preferably has a structure that allows impregnationof the rubber composition into the space among the fiber filaments andformation of a continuous layer between the filament fibers and therubber composition over a relatively longer range in a wider area.Accordingly, the diameter or the maximum width of the filament fiber ispreferably in the range of 0.1 to 100 μm and more preferably 0.1 to 50μm. However, the shape of the cross-section may be or may not becircular and the fiber may be a hollow fiber having a cavity inside.

The length of the filament fiber is preferably 8 mm or more and morepreferably 10 mm or more. If the length of filament fiber is less than 8mm, it is more difficult to entangle the fiber filaments sufficientlyand thus the resulting web does not have the strength required forreinforcement layer.

The basis weight of the non-woven fabric (weight per 1 m²) is preferablyin the range of 10 to 300 g and more preferably 10 to 200 g. If thebasis weight of non-woven fabric is less than 10 g, the non-woven fabricprovide a web having a more irregular surface, it is not preferable asit become difficult to maintain the uniformity of fiber dispersion,leading to fluctuation in the strength, rigidity, and elongation atbreak of the rubber/non-woven fabric composite after vulcanization.Alternatively, if it is more than 300 g, the rubber compositionpenetrates less easily into the non-woven fabric, though it mightdepends on the fluidity of rubber composition, which is not favorablefrom the viewpoints of the peeling resistance of rubber/non-woven fabriccomposite and the like.

In the invention, a film containing a metal or metal compound reactivewith sulfur is formed on the reinforcing material surface. The film isformed so that the oxygen concentration in the film increases in thethickness direction toward reinforcing material.

The metal or metal compound reactive with sulfur is not particularlylimited if it is a material that reacts with sulfur in the rubbercomposition in a vulcanization reaction during rubber vulcanization andexamples thereof include metals such as Co, Cu, Zn, Cr, Al, Ag, Ni, Pb,Ti, and W, or alloys of two or more of these metals; the oxides,nitrides, carbides, sulfides, and sulfates thereof; and the like. Inparticular, metals, alloys, or the oxides thereof such as Co, Co/Cralloy, Cu/Zn alloy, and Cu/Al alloy are preferably used. Co and Co oxideare more preferable (see, Japanese Patent Application Laid-Open Nos.62-87311, 62-246278, and 1-290342). Here, the compounds such as oxides,nitrides, and carbides may be or may not be prepared stoichiometrically.The ratio of the metal element is preferably higher than thestoichiometric value.

The method of forming a film containing the metal or metal compoundabove on the reinforcing material surface is not particularly limited,and may be a liquid-phase deposition method such as plating method andsol-gel method, but the film is preferably formed by a gas-phasedeposition method such as physical vapor deposition (PVD) or chemicalvapor deposition (CVD). The gas-phase deposition methods have advantagesthat they do not cause environmental pollution as they employ no solventand the clogging often encountered in liquid-phase deposition when anon-woven fabric is used.

Examples of the PVD methods include vacuum vapor deposition such asresistance-heating vapor deposition, electron beam-heating vapordeposition, and laser-heating vapor deposition; sputtering such asdirect current sputtering, high-frequency sputtering, magnetronsputtering, ECR sputtering, and ion beam sputtering; ion plating such ashigh-frequency ion plating and cluster ion beam; molecular beam epitaxy;laser abrasion; and the like. Alternatively, examples of the CVD methodsinclude thermal CVD methods such as atmospheric pressure CVD and reducedpressure CVD; plasma CVD methods such as direct current plasma CVD,high-frequency plasma CVD, microwave plasma CVD, and ECR plasma CVD;organic metal CVD; and optical CVD methods. Among these methods, thesputtering method is preferably used and a magnetron sputtering methodis used particularly preferably in the invention.

The first reason for the advantage of using the sputtering method isthat it allows low-temperature film forming on the reinforcing materialsurface. The second reason is that the operational pressure during filmforming is normally relatively high at 5×10⁻² to 1×10¹ Pa and thus thefilm formation is less vulnerable to the influence by the out gas fromthe non-woven fabric or the like. The third reason is that the particlessputtered from the target are possibly scattered by an environmental gassuch as argon (Ar) or the like before directly reaching the reinforcingmaterial surface, causing “wrap-around”. Namely, by the “wrap-around”, afilm is preferably formed on the area not directly facing the target andthe area hidden on the reinforcing material having a complicated shape.

During sputtering, oxygen, which is a reactive gas, is introduced asneeded to the environmental gas, an inert gas such as Ar, He, Ne, or Kr.A nitrogen gas such as N₂ or NH₃ or a hydrocarbon gas such as CH₄ may beadded to the gas. The mixing ratio of the inert gas to the reaction gas(volume ratio in supply gas) is 100/0 to 0/100 (inert gas/reaction gas)and preferably 100/0 to 20/80.

In addition, a bias voltage may be applied to the reinforcing materialas needed. In such a case, either a direct current or an alternatecurrent may be used as the bias current. When an alternate current isused, the alternate current has preferably a pulsed wave or a radiofrequency wave (rf). When a direct current is used, the voltage ispreferably in the range of −1 to +1 kV.

The gas pressure is not particularly limited if sputtering is possible,but preferably 1×10⁻² to 5×10² Pa, more preferably 5×10⁻² to 1×10¹ Pa.The frequency of the power source (supplied to the target) may be thatof the known direct or alternate current. Generally, a direct current orradio-frequency (rf) power source is used, but a pulsed power source maybe used instead. So-called ionized magnetron sputtering that activatesparticles during sputtering by generating inductive plasma between thetarget and the base material may also be used.

In order to provide the film with an inclination in oxygen concentrationby using the film-forming method above, the film may be formed bycontrolling the film-forming conditions such as the film-forming time,ratio of gas supply, and the like, or may be formed by laminating two ormore layers different in the ratio of the composition of metal andoxygen therein. In order to make the oxygen concentration in the filmincrease in the thickness direction toward reinforcing material, theoxygen concentration of the layer at the reinforcing material sideshould be larger than that of the layer at the film surface side. Tomaximize the advantageous effects of the invention, the ratio of oxygenconcentration to metal concentration in the layer at the reinforcingmaterial side of the film is preferably 1.5 times or more larger thanthe ratio of oxygen concentration to metal concentration in the layer atthe film surface side.

The thickness of the film thus formed is not particularly limited, butis preferably 0.6 to 20 nm and more preferably 1 to 10 nm.

The surface of the reinforcing material is preferably cleaned thoroughlyas needed before film forming, and a plasma treatment, ion implantation,ion irradiation, thermal treatment or the like may be performedadditionally after film forming for improvement in the surface state,reactivity, internal stress, and the like of the film. Solvent washingor a combination of solvent washing and a discharge treatment may bepreferably used as the cleaning method. In addition, several cleaningmethods may be used in combination for improving the cleaning effect.

The rubber composition for use in the invention is not particularlylimited and favorable examples thereof include rubber compositionscommonly used as tire, belt, hose, and the like. Accordingly, the rubbercomposition may contain a natural rubber or a synthetic rubber as theprimary component, and additionally a vulcanizing agent, vulcanizationaccelerator, reinforcing material, antioxidant, softener, or the like asneeded.

In adhering a reinforcing material having the film above formed to arubber composition, the reinforcing material is first covered with anunvulcanized rubber composition. Methods of covering the reinforcingmaterial with the unvulcanized rubber composition include the methods ofpressing a sheeted unvulcanized rubber composition on one face or bothfaces of the reinforcing material by a press or roll; applying a liquidcontaining an unvulcanized rubber composition dissolved or dispersed ina solvent onto the reinforcing material; and the like.

After the reinforcing material is covered with the unvulcanized rubbercomposition, the composite is then vulcanized. The optimal condition forvulcanization is selected suitably according to the size, shape,composition, and the like of reinforcing material and unvulcanizedrubber composition which are the subject of vulcanization.

The rubber-based composite materials according to the invention obtainedin this manner may be preferably used for rubber articles that demandboth superior initial adhesiveness and adhesion durability, and examplesthereof include tire, belt, hose, antivibration material, antivibrationrubber, rubber crawler, and the like, although the invention is notparticularly limited thereto.

EXAMPLES

Hereinafter, the present invention will be described with reference toExamples.

Examples 1 and 2 and Comparative Examples 1 and 2

The surface (both surfaces) of a non-woven fabric (fiber: PET [Tetoron(registered trademark), manufactured by Toray Industries, Inc.],physical properties: fineness 6.6 Dtex, specific density: 1.38,strength: 5.3 g/Dtex, breaking elongation: 50%, fiber diameter: 25 μm,basis weight: 60 g/m², and thickness: 5 mm) was cleaned by alow-pressure plasma method under the condition shown in the followingTable 1, and then subjected to sputtering by using a Co target (purity:3N) under the condition also shown in Table 1, to form a film of Co andthe oxide thereof on one face. The average electric densities duringcleaning and film forming in the Table were electric powers supplied toper 1 m³ of non-woven fabric. Separately, in Comparative Examples, thenon-woven fabric of Example 1 was processed under the conditions shownin Table 1 to form a Co film or the oxide film on one face. TABLE 1Surface treatment condition Cleaning condition Film-forming conditionElectric Electric Film-forming Pressure density Period Gases andPressure density period Gas (Pa) (W/m²) (sec) the ratio (Pa) (kW/m²)(sec) Example 1 Ar 100 600 300 1^(st) layer Ar/O₂ = 50/0 0.7 11.5 202^(nd) layer Ar/O₂ = 40/10 0.7 11.5 40 Example 2 Ar 100 600 300 1^(st)layer Ar/O₂ = 50/0 0.7 11.5 20 2^(nd) layer Ar/O₂ = 35/15 0.7 11.5 40Comparative Ar 100 600 300 1^(st) layer Ar/O₂ = 50/0 0.7 11.5 60 Example1 Comparative Ar 100 600 300 1^(st) layer Ar/O₂ = 40/10 0.7 11.5 60Example 2

The element ratios of Co and O of the surface side and a non-wovenfabric side of each film formed under the conditions above weredetermined by using an XPS (Quantum 2000, manufactured by Alpack PhiCo., Ltd.). Results are summarized in Table 2. TABLE 2 Co/O elementratio Co/O Element ratio Example 1 Surface side 95/5  Non-woven fabricside 85/15 Example 2 Surface side 95/5  Non-woven fabric side 80/20Comparative Example 1 Surface side 95/5  Non-woven fabric side 95/5 Comparative Example 2 Surface side 85/15 Non-woven fabric side 85/15

Each of the non-woven fabrics formed under the conditions shown in Table1 was sandwiched with two rubber sheets of 5 mm in thickness having thecomposition shown in Table 5, and the composite was vulcanized undereach conditions of 145° C. for 10 minutes and 145° C. for 30 minutes, togive a rubber-based composite material. Then, each rubber-basedcomposite material was cooled at room temperature and the initialadhesiveness thereof was evaluated immediately. In addition, eachrubber-based composite material vulcanized under the condition of 145°C. for 30 minutes was deteriorated in an oxygen atmosphere and left tostand until the water adhered on the surface is sufficiently evaporated,and then the adhesion durability of each composite material wasevaluated. These results are summarized in Tables 3 and 4.

The evaluation of the initial adhesiveness and the adhesion durabilitywas performed by peeling the rubber sheet of both sides under thecondition of room temperature and a tension speed of 300 mm/min by usingAutograph (manufactured by Shimadzu Corp.) and visually observing therubber adhesion area on the fiber of the non-woven fabric which appearedin the fracture side. Adhesiveness was rated in 10 levels, from level 10when the rubber adhesion area rate is 100% to level 1 when it is 10%.TABLE 3 Evaluation of initial adhesiveness 145° C. for 10 minutes 145°C. for 30 minutes Vulcanization condition Adhesiveness AdhesivenessExample 1 8 9 Example 2 8 9 Comparative Example 1 8 9 ComparativeExample 2 3 8

TABLE 4 Evaluation of adhesion durability 145° C. for 30 minutesVulcanization condition Adhesiveness Example 1 6 Example 2 7 ComparativeExample 1 2 Comparative Example 2 6

TABLE 5 Composition of the rubber composition used in Examples ComponentParts by weight Product name Natural rubber 100 — Carbon black 60 —Stearic acid 2 — Zinc white 5 — Antioxidant 2 Nocrac 6C, OuchishinkoChemical Industrial Co., Ltd. Vulcanization 1 Nocceler NS-P, Ouchishinkoaccelerator Chemical Industrial Co., Ltd Sulfur 2 —

As apparent from Tables 3 and 4, the rubber-based composite materials ofExamples 1 and 2 showed an excellent initial adhesiveness and anexcellent adhesion durability under any vulcanization conditions,because the film was formed on the surface of non-woven fabric which isreinforcing material so that the oxygen concentration therein increasedin the thickness direction toward the non-woven fabric surface. Incontrast, the rubber-based composite material of Comparative Example 1has an initial adhesiveness similar to those of Examples in any of thevulcanization conditions but was inferior in adhesion durability tothose of Examples. Alternatively, the rubber-based composite material ofComparative Example 2 was superior in adhesion durability but inferiorin the initial adhesiveness under the vulcanization condition of 145° C.for 10 minutes, indicating that it does not show a sufficiently highinitial adhesiveness under a wide range of vulcanization condition.

As described above, the present invention provides a rubber-basedcomposite material excellent both in initial adhesiveness and adhesiondurability under a wide range of vulcanization condition.

It should be understood that the foregoing description of the inventionis intended merely to be illustrative of the preferable embodiments byway of example only and that other modifications, embodiments, andequivalents may be apparent to those skilled in the art withoutdeparting from its spirit.

1. A rubber-based composite material comprising a rubber compositionand, adhered thereto, a reinforcing material having a film containing ametal or a metal compound capable of reacting with sulfur formed on thesurface of the material, characterized in that the oxygen concentrationin the film increases toward the reinforcing material in the thicknessdirection.
 2. The rubber-based composite material according to claim 1,characterized in that the film is a laminate of two or more layersdifferent in ratio of the composition of metal and oxygen.
 3. Therubber-based composite material according to claim 1, characterized inthat the ratio of oxygen concentration to metal concentration in thelayer at the reinforcing material side of the film is preferably 1.5times or more larger than the ratio of oxygen concentration to metalconcentration in the layer at the film surface side.
 4. The rubber-basedcomposite material according to claim 1, characterized in that thereinforcing material comprises an organic fiber.
 5. The rubber-basedcomposite material according to claim 4, characterized in that theorganic fiber comprises at least one of polyester and polyamide.
 6. Therubber-based composite material according to claim 1, characterized inthat the reinforcing material is a non-woven fabric.
 7. The rubber-basedcomposite material according to claim 1, characterized in that the filmis formed by physical vapor deposition (PVD) or chemical vapordeposition (CVD).
 8. The rubber-based composite material according toclaim 7, characterized in that the physical vapor deposition (PVD)method is a magnetron sputtering method.
 9. The rubber-based compositematerial according to claim 1, characterized in that the metal or metalcompound is cobalt or cobalt oxide.
 10. A rubber article, characterizedin using the rubber-based composite material according to claim 1.